Following the surgical removal of a hollow vessel portion, e.g. with an intestinal resection due to a tumor having affected a bowel section, the two hollow vessel portions have to be reconnected at their opened ends in such a manner that a continuous pathway is produced. This is referred to as end-to-end anastomosis. As a standard, the two opened ends are reattached to each other with clip suturing devices.
In particular with operations on the small and large intestines, leaky suture connections (suture insufficiency) occur from time to time, which are associated with a serious progress of disease and a high mortality rate, too.
An alternative to stitching the hollow vessel portions is thermofusion technology (TFT). Thermofusion by means of high frequency technology (HF) is based on the denaturation of proteins which are contained in many tissue types. This allows to weld collagen-containing tissue. During the welding process, the tissue is heated up to temperatures above the protein denaturation temperature, and together with the intra- and extracellular matrix is converted into a gel-like state. After compression of the tissue faces, the liquefied tissue cools down to a fused mass, effecting a reliable connection of the tissue.
For the purpose of welding the hollow vessel portions, the tissue grasped between two clamping jaws is exposed to electrical current which flows between electrodes provided on the two clamping jaws.
For preventing the sealing or welding from breaking down, the parameters acting on the tissue have to be detected and controlled. In order to ensure this, a precise control of temperature, pressure, tissue impedance, distance and position is required.
It is desirable to realize a uniform treatment of the tissue which is held between the clamping jaws, so that all zones are reliably reached and no zone is exposed to an excessively high current. To this end, it has to be ensured that the HF electrodes are uniformly spaced from each other and aligned so as to be parallel to each other.
The prior art does not disclose any instruments of suitable size for being used for the above-mentioned hollow vessels and tissue types. With regard to coagulation instruments of smaller size, as shown e.g. in EP 1 747 762 A2, a non-parallel alignment of the HF electrodes occurs during closing the clamping jaws, which is due to the type of construction.
Related state of the art is known from the documents DE 20 2004 009 427 U1 and DE 699 29 230 T2.
The distance between the electrodes can be maintained by spacers which are attached to the clamping jaws. If however, a higher number of spacers is provided on the clamping jaws, as is shown for instance in EP 1 656 901 B1, EP1 952 777 A1, EP 1 372 507 A1 or US 2004/122423 A1, it is inevitable that the tissue is perforated by the spacers, as it will be compressed under the spacers in the closed state of the clamping jaws such that there will be permanent tissue damage. This has negative effects on the result of the sealing process.
If the contact pressure of the clamping jaws is reduced in order to avoid any perforation of the tissue, and if the tissue is only clamped under the spacers, this leads to an angular deflection of the clamping jaws.
As the spacers are further made from an electrically non-conductive material for avoiding a short-circuit between the HF electrodes, a so-called coagulation shade develops in the vicinity of said spacers, which means that the tissue portions are encapsulated in the vicinity of or under the spacers, hence are not supplied with electrical current or only to an insufficient extent, and an unsatisfactory welding of the vessel portions will occur.
If the number of the spacers is reduced, it is inevitable that the distance between the individual spacers increases. If the clamping jaws are pressed against each other with high contact pressure, the clamping jaws and the electrodes will be bent between the spacers even if stiff materials are used, so that distance of the electrodes is smaller between the spacers than at the spacers. These differences in the distances of the electrodes results in a non-homogenous penetration of the tissue with HF energy.